When you sign up for a Zoho account, you will register using an email account. That email address will be your Primary email address.
When you create an email account in Zoho Control Panel, that email address may be already registered for some other account. In such a case, an invitation email will be sent to the other Zoho account, requesting the user to join your Organization.
Once the user accepts the invitation, they will be a part of your organization.
